Logging devices which measure formation properties based on nuclear measurement are known. Typically, the logging device includes a nuclear source and spaced Geiger-Muller detectors or scintillating crystals associated with photomultiplier tubes mounted in a pad that is applied against a bore hole wall.
However, such logging devices are not reliable in hostile environment (high temperature, high pressure). Further, they require high polarization voltage which is not easy to provide with regards to down-hole conditions. Finally, they are not adapted for performing pixelized density imaging of a geological formation.